interface A {
	double f(double x,double y);
}
class B implements A {
	public double f(double x,double y) {
		return x*y;
	}
	int g(int a,int b) {
		return a+b;
	}
}public class E {
	public static void main(String args[]) {
		A a = new B();
		System.out.println(a.f(3,5));   //【代码1】
		B b = (B)a;
		System.out.println(b.g(3,5));   //【代码2】
	}
}

